Photoreceptors used in electrostatographic printing machines are typically fabricated by a dip coating method where the substrate is engaged with a chuck apparatus at the top of the substrate and the chuck apparatus forms a hermetic seal with the inner surface of the substrate which traps air inside the substrate when it is dipped into the coating solution. The trapped air provided by the hermetic seal prevents the coating solution from coating the substrate's inner surface. The conventional dip coating method coats only the outer surface of the substrate (even with a hermetic seal, a small portion of the inner surface adjacent an end of the substrate may be coated by the coating solution) during the fabrication of the photoreceptor. The problem with creating a hermetic seal is that the trapped air may vibrate like a spring due to its compressibility during the dip coating, potentially causing coating nonuniformities in the thickness of the coated layer--the chatter line defect. The present inventors have found that the tendency for the trapped air to vibrate during dip coating increases with larger substrates, thinner substrate walls, and lower viscosity coating solutions. Complicated chuck designs or thick walled substrates can be used to overcome the vibration problem, which undesirably increase costs or limit the type of substrates that can be used. In addition, the trapped air can also leak out and cause a coating defect, called burping. There is a need, which the present invention addresses, for new dip coating methods which minimize or avoid the problems described above.
Conventional methods for fabricating photoreceptors, including descriptions of suitable chuck apparatus, are described in Swain, U.S. Pat. No. 5,681,392; Petropoulos et al., U.S. Pat. No. 5,633,046; Petropoulos et al., U.S. Pat. No. 5,578,410; Swain et al., U.S. Pat. No. 5,520,399 and Swain et al., U.S. Pat. No. 5,688,327.